Historically, the primary mode of reducing power consumption in electronic circuits has been to aggressively scale down the power supply voltage. This power supply reduction follows naturally for CMOS technologies since the Moore's Law scaling of processes into the nanometer range has resulted in gate oxide breakdown voltages on the order of 3.3 volts, 2.5 volts, 1.8 volts and lower. While effective in mitigating power consumption, this reduced breakdown voltage places significant limitations on the interconnection of these devices with other higher voltage systems. Such high voltage systems include 5 volt Legacy hardware and 28 volt aerospace hardware.
A typical solution to this problem is to add intermediate control circuitry between the integrated circuit and the external high voltage system. In this manner the system logic is performed at efficient low voltage levels, while the output is driven from an external source. This solution is viable, however the size and complexity of the overall design is increased considerably. A second typical solution is to use an integrated circuit process that is capable of laying down thick as well as thin gate oxides. This enables low voltage as well as high voltage transistors to be laid down on the same substrate. However, this alteration of the original fabrication process is prohibitively expensive in many applications. Further both of these solutions suffer from another problem—something external to the desired integrated circuit fabrication process must be added to the final design. In extreme environment applications (i.e. high temperature, low temperature, high radiation, high pressure, corrosive, etc.) this is not always acceptable. The integrated circuit fabrication process has been chosen for its temperature, radiation, and pressure characteristics. By adding external devices or altering the fabrication process these required characteristics can be lost.
This invention arose out of a need to develop a high voltage to low voltage logic level shifters that can be fully integrated onto the same substrate as the low voltage logic circuitry that controls it. That is, without altering the fabrication process in any way, this invention creates a means by which to control high voltage signals that exceed the breakdown voltage of the process used for fabrication.